It is well known to employ various intravascular endoprostheses delivered percutaneously for the treatment of diseases of various body vessels. These types of endoprosthesis are commonly referred to as stents. A stent is a generally formed longitudinal tubular device of biocompatible material, such as stainless steel, cobalt-chromium, nitinol or biodegradable materials, having holes or slots cut therein so they can be radially expanded, by a balloon catheter or the like, or alternately self-expanded within the vessel. Stents are useful in the treatment of stenosis, strictures or aneurysms in body vessels such as blood vessels. These devices are implanted within the vessel to reinforce collapsing, partially occluded, weakened or abnormally dilated sections of a vessel. Stents are typically employed after angioplasty of a blood vessel to prevent restenosis of the diseased vessel. While stents are most notably used in blood vessels, stents may also be implanted in other body vessels such as the urogenital tract and bile duct.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, the stent configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent can be accomplished by inflation of a balloon attached to the catheter, or alternatively using self-expanding materials such as nitinol within the stent. Examples of various stent constructions are shown in U.S. Pat. No. 4,733,665 filed by Palmaz on Nov. 7, 1985, which is hereby incorporated herein by reference.
A balloon angioplasty can be used in place or as an adjunct to a stent implant. As is well known, a balloon is deployed in a narrowed blood vessel and expanded to open up the narrowed vessel. Once the vessel has regained sufficient flow, the balloon is withdrawn.
With either of these techniques, restenosis may develop subsequent to the procedure in about half of the patient receiving a stent. Restenosis is believed to be even higher for angioplasty. To reduce the rate of restenosis, drug eluting stents are provided, which has been shown to be superior to bare metal stents in reducing the restenosis. However, thrombosis for drug eluting stent has been shown to be problem over time, believed to be as much as five years or longer. Additionally, the polymer carrier for the drug in such drug eluting stent is believed to be a source of the inflammatory response or local toxicity by the body vessel.